Precision insert for molding multi-fiber connectors and method for manufacturing thereof

ABSTRACT

A guide block assembly for aligning and retaining fiber bore forming pins and guide pin bore forming pins in precise relation to each other during the molding of a multi-fiber ferrule includes a unitary member defining at least one fiber bore and at least one guide pin bore. Each fiber bore, and optionally each guide pin bore, is formed by creating a starter hole using a first electric discharge machining (EDM) wire and enlarging the starter hole using a second EDM wire. Each fiber bore has a length to diameter ratio of between approximately 3::1 to 10::1, more preferably between approximately 4::1 to 8::1, and most preferably approximately 6::1. The guide block assembly may further include a cavity behind the fiber bore and a front face that forms a non-rectilinear surface on the face of the ferrule. The unitary block assembly contains fewer parts and is less expensive to manufacture.

[0001] This application is a continuation-in-part of co-pendingapplication Ser. No. 09/621,226, filed on Jul. 21, 2000. Priority tothis application is hereby claimed under 35 U.S.C. § 120, and theco-pending application is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to an apparatus and amethod for molding multi-fiber optical connector ferrules.

BACKGROUND OF THE INVENTION

[0003] A fiber optic cable may include one or more optical fiberscapable of transmitting audio, video or other information. Examples ofoptical fibers are disclosed in U.S. Pat. Nos. 5,561,730 and 5,457,762.Fiber optic cables are laid over long distances and require opticalconnectors or ferrules to link discrete segments of the optical fibers.As used herein, the term “ferrule” refers to a plug assembly or astructure that receives a terminal end of an optical fiber or opticalfiber ribbon and then abuts against an opposing ferrule to aligncorresponding optical fiber or ribbon for transmission of an opticalsignal or signals.

[0004] An example of an optical ferrule is disclosed in U.S. Pat. No.5,214,730 to Nagasawa et al. FIG. 1 illustrates an optical ferrulesimilar to that depicted in Nagasawa, and shows multi-fiber ferrules 3and 3′ connected to optical fiber ribbons 1 and 1′, respectively. Ribbon1 comprises multiple optical fibers 2 to be aligned with correspondingoptical fibers 2′ (not shown) from ribbon 1′. Ferrule 3 defines aplurality of optical fiber bores adapted to receive fibers 2 and twoguide pin bores 4 adapted to receive guide pins 6. Guide pins 6 alignferrule 3 with ferrule 3′, when the two ferrules are connected to eachother to align optical fibers 2 and 2′ to optimize optical transmission.

[0005] During a typical molding process to produce ferrules 3, boreforming pins are inserted through the mold cavity to create the guidepin bores and the optical fiber bores in the ferrules. Molten plastic isthen injected into the mold cavity, and after the plastic solidifiessufficiently the pins are withdrawn to form the bores in the ferrules toreceive the optical fibers and guide pins. Prior to connecting toferrule 3, optical ribbon 1 is stripped of its outer matrix coating andits buffer layer to expose fibers 2. The individual fibers 2 areinserted into the fiber bores on ferrule 3. Various well-knowntechniques are used to permanently affix fibers 2 to ferrule 3. Endfaces 5 and 5′ of ferrules 3 and 3′ are then polished along with theexposed ends of fibers 2. A pair of guide pins 6 is then inserted intoguide holes 4 to connect and align the ferrules. A spring clip (notshown) may be used to clamp the two ferrules together.

[0006] There is a premium placed on the precise alignment of opposingoptical fibers at a connection to minimize signal losses, whichdiminishes the quality of the optical transmission through theconnection. The precision of aligning opposing optical fibers is moresensitive with multi-fiber ferrules due to the presence of multipleoptical fibers and to each fiber's location relative to each other andrelative to the guide pins within the ferrules. Additionally, when anoptical fiber is a single-mode fiber, i.e., the optical signal istransmitted through only a small portion of the fiber, the alignmentneeds to be even more precise.

[0007] A conventional ferrule molding method uses a series of V-shapedopen grooves machined into a block of the mold cavity to retain the boreforming pins inserted into the mold cavity. FIG. 2 shows across-sectional view of this conventional molding method, where fiberbore forming pins 7 and guide pin bore forming pins 8 are shown disposedin V-shaped grooves 9. The disadvantages of this or similar open grooveconstructions include a tendency of the pins 7 and 8 to float within theV-shaped grooves in the direction of arrow A during the molding process.This float contributes to imprecise alignment of the bores formed in themolded ferrule. Additionally, after repeated uses of a mold cavity withthis groove construction, flash begins to build up in areas indicated byB. This flash build up requires frequent cleaning of the grooves. Also,as can be seen, pins 7 contact the V-shaped grooves only along two linesof contact and thus all the friction forces of the repeated insertionand removal of the pins are imparted along these two lines of contact,thereby causing uneven wear along the sides of the V-shaped groove. Thiscauses the alignment of the pins to become progressively more imprecise.

[0008] The drawbacks of the molding process with the V-shaped grooveshave been addressed by the “small hole technology” disclosed by U.S.Pat. No. 5,786,002 to Dean et al. As shown in FIG. 3, Dean et al.discloses a guide block assembly comprising a plurality of fiber boreblocks 12, at least two guide pin bore blocks 14 and a plurality ofspacer blocks 16 arranged in any desirable configuration in a moldcavity. Each fiber bore block 12 defines a small hole or bore 18 adaptedto receive during the molding process a pin having the diameter of anoptical fiber, and each guide pin bore blocks 14 defines a bore 19adapted to receive a pin having a diameter of a guide pin. Moltenplastic is injected into the mold cavity and the pins are thereafterwithdrawn from the holes and the mold cavity to form receptacles in theferrules to receive optical fibers 2 or guide pins 6. The use of boresmore precisely retains the pins during the molding process than the useof V-shaped open grooves. Dean et al. resolves the known drawbacks fromthe V-shaped open groove molding technique, and provides the additionalbenefits of establishing precise spatial relationship among the modularblocks, by machining the surfaces of the adjoining blocks.

[0009] Dean et al., however, requires the fabrication of multipleblocks, which increases the costs and may become less economical whenused to fabricate ferrules for a small number of optical fibers. Hence,there remains a need in the art for a molding apparatus that has theadvantages realized in the Dean et al. '002 patent, but requires fewercomponents and is more economical to produce.

SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the present invention to providea device for molding multi-fiber ferrules using small hole technology.

[0011] Another object of the invention is to minimize the costs offabricating a device for molding multi-fiber ferrules.

[0012] Yet, another object of the invention is to provide a devicecapable of precisely aligning and retaining the bore forming pins duringthe molding of multi-fiber ferrules.

[0013] These and other objects of the present invention are accomplishedby a guide block assembly for aligning and retaining at least one fiberbore forming pin and at least one guide pin bore forming pin during themolding of a ferrule. The guide block assembly comprises a unitarymember defining at least one fiber bore and at least one guide pin bore.The fiber bore is created by an electric discharge machining (EDM) wire.One starter hole is created for each bore with the EDM wire attached atone end to an EDM machine. The starter hole is then enlarged by a secondEDM wire connected to an EDM machine at both ends.

[0014] The ratio between the length of the fiber bore to its diameter ispreferably from approximately 3::1 to 10::1, more preferably fromapproximately 4::1 to 8::1, and most preferably approximately 6::1. Inaccordance with another aspect of the invention, the unitary guide blockassembly has a front face, wherein the front face is altered to form anon-rectilinear surface. The non-rectilinear surface can be a curvesurface, a stepped surface, an angled surface, or a pedestal surface,among others.

[0015] In accordance with other aspects of the invention, an open cavitybehind the fiber bore is provided to reduce the flash build-up, andlongitudinal slots are formed around the fiber bore to reduce the wearand tear on the bore forming pins.

[0016] In accordance with another aspect of the invention, a method forfabricating a guide block assembly defining at least one fiber bore foraligning and retaining at least one fiber bore forming pin during amolding of a ferrule is provided. This method comprises the steps ofsecuring a blank to a wire electric discharge machining (EDM) machine,forming a starter hole in said blank with a wire attached at one end tothe EDM machine, and enlarging said starter hole to a predetermined sizeand dimension of the fiber bore. The enlarging step may comprise thesteps of threading a second wire through the starter hole, andconnecting both ends of the second wire to an EDM machine (which may bea different EDM machine) to enlarge the starter hole. This method mayalso comprise the step of forming a non-rectilinear surface on a frontsurface of the guide block assembly before or after the fiber bore isformed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is illustrated by way of example in theaccompanying drawings, in which:

[0018]FIG. 1 is a perspective view of a pair of conventional multi-fiberoptical connector ferrules;

[0019]FIG. 2 is a cross-sectional view of a conventional V-shaped opengroove guide block assembly;

[0020]FIG. 3 is front view of another prior art guide block assembly;

[0021]FIG. 4 is a perspective view of a representative arrangement of amold cavity environment illustrating a preferred embodiment of a guideblock assembly of the present invention;

[0022]FIG. 5 is an exploded view showing the top and bottom portions ofthe guide block assembly of the present invention;

[0023]FIG. 6 is an enlarged front view showing an array of fiber boresand guide pin bores of the guide block assembly of the presentinvention;

[0024]FIG. 7 is a cross-sectional view of the bottom portion of theguide box assembly along line7-7 shown in FIG. 5;

[0025]FIG. 8 is a top view of the bottom portion of the guide blockassembly showing another aspect of the invention;

[0026]FIG. 9 is a longitudinal cross-sectional view of a fiber bore witha fiber bore forming pin inserted therein;

[0027]FIG. 10 is a front view of an alternative embodiment of thepresent invention;

[0028]FIG. 11 is a front view of another alternative embodiment of thepresent invention;

[0029]FIG. 12 is a perspective front view of another embodiment of thepresent invention;

[0030]FIG. 13 is a perspective back view of the embodiment shown in FIG.12;

[0031]FIG. 14 is a top view of the embodiment shown in FIGS. 12 and 13;

[0032]FIG. 15A is a front view of the embodiment shown in FIGS. 12, 13and 14, and FIG. 15B is an enlarged view of a portion of FIG. 15A;

[0033]FIG. 16A is a front view of the alternative embodiment of thepresent invention, and FIG. 16B is an enlarged view of a portion of FIG.16A;

[0034] FIGS. 17A-E illustrate variations of the end face of the ferruleproduced by embodiments of the guide block assembly of the presentinvention; and

[0035] FIGS. 18A-B are enlarged views of a portion of the guide blockassembly showing the milled front face.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Referring to the drawings, wherein reference numbers are used todesignate like parts, FIG. 4 shows one preferred embodiment of the guideblock assembly 20, disposed in a mold cavity 22 to illustrate theenvironment for the guide block assembly 20. Assembly 20 has a mold face24, which can serve as one of the walls 26 defining mold cavity 22.

[0037] Referring to FIG. 5, assembly 20 comprises a top portion 28 and abottom portion 30. Top portion 28 defines on its lower surface a numberof semi-circular guide pin bore grooves 32 a and a number ofsemi-circular fiber bore grooves 34 a. As illustrated by FIG. 5, fiberbore grooves 34 a are positioned on the inside of the guide pin boregrooves 32 a. Grooves 32 a and 34 a are sized and configured to matchwith semi-circular guide pin bore grooves 32 b and semi-circular fibergrooves 34 b located on the top surface of bottom portion 30, such thatwhen the top and bottom portions are assembled together, thesemi-circular fiber bore grooves 34 a and 34 b are joined to form fiberbores 34 and semi-circular guide pin bore grooves 32 a and 32 b arejoined to form guide pin bores 32. The top portion 28 also defines twovertical channels 36 a corresponding to vertical channels 36 b definedon the bottom portion 30, such that conventional fasteners such as nutsand bolts may clamp the top portion 28 to the bottom portion 30.

[0038] Additionally, the top and bottom portions 28 and 30 may have apair of corresponding key pin grooves 35 a and 35 b, respectively, asillustrated in FIG. 5. Key pin grooves 35 a and 35 b together form keypin bore 35 adapted to receive a key pin when the top and bottomportions 28 and 30 are assembled. The key pin 37 is inserted into bore35 to align the top portion to the bottom portion. The bottom portionmay also have receiving channels 40 disposed on its bottom surface.Receiving channels 40 are sized and dimensioned to receive correspondingbosses on the mold cavity (not shown), such that the guide blockassembly 20 can be securely affixed onto the mold cavity. Also, top andbottom portions 28 and 30 may also have through holes 42 and 44, whosefunction is described below.

[0039]FIG. 6 is an enlarged exemplary view of the assembly 20 showingthe relative dimension and location of guide pin bore grooves 32 a and32 b in relation to fiber grooves 34 a and 34 b. Although, only two setsof guide pin bore grooves and fiber grooves are shown, any number ofgrooves can be defined by assembly 20. FIG. 7 shows a cross-sectionalview of bottom portion 30 illustrating by example the location of theguide pin bore grooves 32 b, channels 36 b and key pin groove 35 b inrelation to each other.

[0040] In accordance with another aspect of the invention illustrated inFIG. 8, the length of the fiber bores 34 is kept relatively shortrelative to its diameter, and an open cavity or space 39 is providedbehind the bores 34, such that the molding residue can be pushed throughthe bores on repeated molding cycles and collect in the open cavity orspace 39 instead of clogging the fiber bores. While the open cavity orspace 39 is illustrated on bottom portion 30, it may also be on the topportion 28 or both. The preferred ratio between the length and diameterof the fiber bore is approximately between 3::1 and 10::1; the morepreferred ratio is approximately between 4::1 to 8::1; and the mostpreferred ratio is approximately 6::1.

[0041] Guide block assembly 20 is configured to retain a plurality offiber bore forming pins 50 receivable in fiber bores 34 and retain guidepin bore forming pins 51 receivable in guide pin bores 32, as shown inFIG. 4. Any suitable jig, not shown, can be used to hold and to movepins 50 and 51 into and out of bores 34 and 32, respectively. During themolding of a multi-fiber ferrule, the pins are inserted into the boresand the molding material is injected into the mold cavity formed in partby walls 24 and 26 around the pins. For example, as shown in FIG. 9, thedistal end portion 52 of a representative fiber bore forming pin 50 ispartially inserted into fiber bore 34 and molding material is injectedinto mold cavity 22 and covers mold zone 54 of fiber bore forming pin 50outside of bore 34. After the mold material sets, the pins are retractedto leave behind a plurality of molded bores in the ferrules. Fiber boreforming pins 50 will create a number of fiber bores sized anddimensioned to receive optical fibers in close tolerance. Since thelocation of the bores 32 and 34 can be precisely machined as describedbelow, and the pins 50 and 51 are held in these precisely positionedbores during the molding process, the molded bores in the ferrulescreated by the withdrawal of the pins are also precisely positioned toreceive the optical fibers and guide pins, especially at the front face24 of assembly 20. It should be noted that the front face of the ferrulewould be formed at the front face 24.

[0042] Fiber bore forming pins 50 may be the actual fibers when theferrules are molded directly around the fibers. As shown in FIGS. 6-8,the guide pin bores 32 and guide pin bore forming pins 51 typicallycreate larger diameter molded guide pin bores than the molded fiberbores to receive the guide pins to align two opposing multi-fiberferrules. The shape of the guide bore forming pins 51 and guide pinbores 32 is shown to be circular. This shape, however, can be any shape,such as oval, triangular or polygonal.

[0043] The present invention is directed to an apparatus and method toprecisely arrange the fiber bore forming pins and the guide pin boreforming pins relative to each other in such a way that the precision isrepeatable over a large number of molding cycles. As discussed in thebackground of the invention, the method of arranging the bores withV-shaped grooves as shown in FIG. 2 suffers from floating of pins, flashbuild up, and premature and uneven wear of the guide block assembly. Byusing pre-arranged bores in the guide block assembly and insertablepins, float and uneven wear are reduced and flash build up issubstantially eliminated. Specifically, bores 32 and 34 provide lessroom than the V-shaped open grooves for the floating of the pins 50 and51 during the molding process. Furthermore, by providing bores thecontact between the pins and the bores is spread out over thecircumferential contact surface between the bores and the pins, therebydecreasing wear on the bores. Additionally, by adopting the preferredrange of ratios between the length and diameter of the fiber bore 34 andby providing an open cavity 39 behind the fiber bores 34 as shown inFIG. 8, the clogging problem is substantially reduced.

[0044] Also by having only a limited number of components, e.g., twoportions 28 and 30 in the above-described preferred embodiment, thepresent invention reduces the costs of fabricating the guide blockassembly over the guide block assembly discussed in Dean et al., whichcomprises a relatively high number of blocks.

[0045] In another aspect of the present invention, the bottom surface ofthe top portion 28 of the guide block assembly 20 and the top surface ofthe bottom portion 30 are mirror images of each other. When the twoportions are clamped or bolted face-to-face together, any remainingmisalignment after the key pin 37 in inserted into the key pin bore 35can be readily detected. Such misalignment would make the diameter ofthe bores in the guide block assembly smaller in the direction from themold face 24 toward the back of the assembly, when the grooves 34 a and34 b are aligned at the mold face but misaligned elsewhere. A simplelapping process performed on the bore can readily remove any suchmisalignment. The lapping process comprises covering a precision gaugewire having a diameter smaller than the bore with a lapping compound,e.g., an abrasive compound such as one-quarter micron diamond grit, andthen using the precision gauge wire with the lapping compound into thebore to remove any misalignments.

[0046] The guide block assembly 20 of the present invention can bemanufactured by machining the semi-circular grooves into a metal orceramic block using known precision grinding techniques. Preferably, thetop and bottom portions 28 and 30 can be manufactured by an electricdischarge machining (EDM) process. A precision wire EDM machine, or morepreferably a submersible wire EDM machine, removes metals from metalblocks by creating thousands of electrical discharges per second thatflow between a wire and the metal blocks, vaporizing metal in thecontrolled area. In the preferred submersible wire EDM machine, azinc-coated brass, molybdenum or tungsten wire of approximately 0.0005to 0.003 inch in diameter is submerged in a tank of dielectric fluid,such as deionized water, along with the metal blocks. As the wire ismoved relative to the metal blocks, semi-circular grooves are formed onthe blocks. Typically, eight to twelve passes from the EDM wire cancreate the preferred fiber pin groove. The motion of the wire may becontrolled by any commercially available computer numerical control(CNC) software. A detailed discussion the EDM processes is provided inthe Machinery's Handbook, by E. Oberg et al, (Industrial Press,1996)(25^(th) edition) at page1266. This discussion is herebyincorporated by reference.

[0047] At least one manufacturing advantage is realized by the fact thatopposing surfaces on the top/bottom portions of the assembly 20 aremirror-images of each other. Hence, regardless of the actualmanufacturing technique used, e.g., grinding, machining, or EDMprocesses, the two corresponding opposing surfaces can be manufacturedat the same time using the same equipment. For example, the bottomsurface of top portion 28 and the top surface of the bottom portion 30illustrated in FIGS. 5 and 6 can be manufactured at the same time bysecuring two metal blanks side by side, and corresponding pairs ofsemi-circular grooves 34 a and 34 b or 32 a and 32 b are created by theEDM wire or by the blade of a cutting tool across the two metal blanks.This ensures that any one pair of grooves is properly cut and positionedon the metal blanks. As discussed above and illustrated in FIGS. 5, 7,and 8, the through holes 42 and 44 provided on the metal blanks aredimensioned and configured to receive fasteners, such as screws or boltsand nuts, to secure the metal blanks together. The holes 42,44 may havecountersinks (not shown) for the fasteners that hold the top and bottomportions 28,30 together during the EDM or machining process.

[0048] By utilizing only a small number of components to construct theguide block assembly while still employing the “small hole technology,”the present invention is able to avoid the drawbacks of the conventionalV-shaped open groove method, and accomplishes the same objectives asDean et al. at lower costs.

[0049] It will also be noted that although only two semi-circular fibergrooves 34 a,b on the top and bottom portions are illustrated in FIG. 5,any number of fiber grooves can be machined on the top and bottomportions. Furthermore, although only one row of fiber bores is shown onguide block assembly 20, the present invention may have any number ofrows, as shown in FIG. 11. The guide block assembly 70 may have aplurality of rows of fiber bores, for example two rows of fiber bores.Assembly 70 comprises three portions: a top portion 72, a middle portion74 and a bottom portion 76. In this example, top portion 72 defines fivesemi-circular fiber grooves on its lower surface to correspond with thefive semi-circular fiber grooves on the top surface of the middleportion 74. Middle portion 74 in turn has three semi-circular fibergrooves and two semi-circular guide pin bore grooves defined on itslower surface to correspond with the three semi-circular fiber groovesand two semi-circular guide pin bore grooves defined on the top surfaceof the bottom portion 76. Hence when the three portions of assembly 70are assembled, a first row of five fiber bores and a second row of threefiber bores disposed between two guide pin bores are formed, as shown.In accordance with the present invention, any number of rows of anynumber of bores can be formed and the guide pin bores can be located onany row using the manufacturing processes described above. For example,the bottom surface of top portion 72 and top surface of middle portion74 can be fabricated at the same time, and the bottom surface of middleportion 74 and top surface of bottom portion 76 can be fabricated at thesame time.

[0050] Alternatively, the guide block assembly can be fabricated from asingle block as shown in FIG. 10 to further reduce the costs offabricating the guide block assembly. Using the wire EDM process, aftera starter bore 62 is first created by conventional techniques such asdrilling, the EDM wire may be inserted in the starter hole and the cut apath 64 to form fiber bores 34. Path 64 may then be filled with a hightemperature epoxy. Guide pin bores 32 may be drilled as shown, or path64 may extend from fiber bores 34 to create guide pin bores 32.

[0051] In accordance with another aspect of the invention, anotherunitary guide block assembly 80 is shown in FIGS. 12-15. Guide blockassembly 80 is made from a single block of material. Unlike the guideblock assembly 60 discussed above, guide block assembly 80 does notrequire the EDM wire to form path 64 to connect the fiber bores and/orguide pin bores together, and therefore obviates the needs to back fillpath 64 with epoxy. As shown, unitary guide block assembly 80 has reliefcavity 39 disposed behind fiber bores 34, as described above. Similar toguide block assembly 20, assembly 80 also has guide pin bores 32disposed to the outside of fiber bores 34, and receiving channels 40sized and dimensioned to received corresponding bosses on the moldcavity (not shown), such that the guide block assembly can be securelyaffixed onto the mold cavity, as discussed above and as illustrated inFIG. 4. Assembly 80 also has front face 24, which serves as one of thewalls of mold cavity 22.

[0052] The advantages of unitary guide block assemblies 80 and 60 overguide block assembly 20 include the elimination of a number ofcomponents, such as key pin bore 35 and key pin 37 to align the twohalves of the guide block assembly, through holes 42 and 44 to clamp thehalves together during the manufacturing process, and the verticalchannels 36 a and 36 b to clamp the halves together during the ferrulemolding process. Additionally, the lapping process to ensure properalignment of the fiber bore grooves is also not necessary.

[0053] Guide block assembly 80 is preferably manufactured by a novel EDMmanufacturing process. First, the relief cavity 39 is cut byconventional method in the blank block. An additional relief channel 82may be provided behind relief cavity 39. Next, a series of starter holesis fashioned into the blank. One starter hole is prepared for each guidepin bore 34 and for each fiber bore 32. Due to the relative sizes ofthese bores, the starter holes for the guide pin bores can be largerthan the starter holes for the fiber bores. The starter holes are formedby a single EDM wire, which is connected to the EDM machine only at oneend. The free end of the EDM wire is positioned at the desired locationand electrical discharges are emitted therefrom to create the starterholes. Advantageously, the starter holes for the fiber bores 34 arelocated opposite from relief cavity 39, where the width of the blank isthinnest, which, in addition to preventing flash build-up, alsofacilitates the creation of the starter holes. After the starter holesare made, a longer continuous feed EDM wire is threaded through eachstarter hole. This longer wire is then connected to the EDM machine atboth end and the electrical discharges from this longer wire are emittedto enlarge the starter hole until the hole reaches the desired size ofthe fiber bore 32. Advantageously, the blank block remains clamped tothe EDM machine during the entire manufacturing process, therebyeliminating possible location and sizing errors due to handling andrepositioning of the blank. The starter holes for the guide pin bores 34may also be created the same way. Due to the relative larger size of theguide pin bores, their starter hole may also be created by conventionalmethods, such as drilling.

[0054] The starter-hole EDM wire typically is 0.0020-0.0025 inch indiameter and 3 mm (0.12 inch) in length. As described above, EDM wiresare typically made from zinc coated brass, molybdenum, or tungsten. Dueto the relative shortness of the wire, it can be formed rigid andstraight, which increase the accuracy of the position and orientation ofthe starter holes. As a result, the fiber holes 32 made in accordancewith this EDM wire method extend in a precise straight line and runningperpendicular to the front surface 24 of the unitary guide blockassembly 80.

[0055] Several advantages directly flow from this EDM wire method.First, due to the ability to pin point the starter hole and then createstraight fiber bores, the radial offset between corresponding opticalfibers from two adjoining ferrules made in accordance with this methodhas been reduced to ¼ μm for single mode fibers and ½ μm for multi modefibers. As discussed above, single mode fiber use only a relativelysmall portion of the fiber's cross-section for signal transmission,while multi-mode fibers use more of the fiber's cross-section. Forexample, a single mode fiber uses approximately 9 μm section of a 125 μmoptical fiber, while a multi-mode fiber uses approximately 50-60 μm ofthe 125 μm optical fiber. Hence, tight control of the radial offsetbetween connecting optical fibers, particularly a single mode fiber, isdesirable and can be achieved by the ferrules made in accordance withthe present invention. Furthermore, the radial offset between the fiberbores 32 and the fiber bore forming pins 50 during the molding operationhas also been reduced to about ½ μm.

[0056] Another advantage realized from the EDM wire method is that dueto the more precise perpendicular orientation of the fiber bores 32relative to the front surface 24 of guide block assembly 80, frontsurface 24 may have an arcuate surface or other non-rectilinear surfacesmilled or otherwise formed thereon, after the fiber bores have beenformed while maintaining the precise location of the fiber bores on themilled front surface 24. In other words, if the fiber bores 32 are notprecisely oriented perpendicular to front surface 24 when front surface24 is milled, the location of the fiber bores 32 on the milled surfacewill shift relative to the location of the fiber bores 32 on thepre-milled surface. This shifting produces inaccurate guide blockassemblies, which in turn produces inaccurate placement of the fibers atthe front face of the ferrules. The fiber bores 32 may also be formedafter the front surface 24 is milled.

[0057] It is known in the art that providing a protruding curve or othernon-rectilinear surfaces on the end face 5 of ferrule 3 positions theterminal ends of the optical fibers 2 forward of the ferrule to reduceback reflectance and improve signal transmission between ferrules.Examples of milled front surface 24 are illustrated in FIGS. 18A and18B. Heretofore, each ferrule is typically ground or polished aftermolding to achieve the curve surface. A unitary milled guide blockassembly in accordance with the present invention obviates the need togrind each ferrule separately, thereby reducing manufacturing costs. Inaddition to a milled curved front face 24, which produces the curved endface 5 in ferrule 3 shown in FIG. 17A, front face 24 may have othershapes milled thereon to produce other shapes for end face 5. Forexample, front face 24 may have a step milled therein, shown in FIG.18A, to produce the stepped face 5 shown in FIG. 17B. Front face 24 mayalso have individual holes milled around each fiber bore 32 to producethe end face 5 shown in FIG. 17C. Front face 24 may also have anelongated channel milled around all the fiber bores 32, shown in FIG.18B, to produce the pedestal end face 5 shown in FIG. 17D, and frontface 24 may have a slant formed thereon to produce the angled end face 5shown in FIG. 17E.

[0058] Additionally, while FIGS. 12-15 show the unitary guide blockassembly 80 with two fiber bores 32 defined thereon, it may have anynumber of fiber bores. For example, unitary guide block assembly 84shown in FIGS. 16A-16B has 12 fiber bores and the ferrules shown inFIGS. 17A-E were made with a guide block assembly defining 4 fiberbores. Hence, this present invention is not limited to any specificnumber of fiber bores.

[0059] In accordance with another aspect of the present invention, aplurality of longitudinal slots may be cut along the periphery of thefiber bores 32 or the guide pin bores 34 to reduce the wear and tear onthe fiber bore forming pins 50 and the guide pin bore forming pins 51.While it remains desirable to evenly distribute the contact between thepins and the bores during the molding process as discussed above, it isalso advantageous to reduce the contact areas between these twocomponents. Preferably, four longitudinal slots disposed along the boresreduce such contact areas.

[0060] While various descriptions of the present invention are describedabove, it is understood that the various features of the presentinvention can be used singly or in combination thereof. Therefore, thisinvention is not to be limited to the specifically preferred embodimentsdepicted therein.

1. A guide block assembly for aligning and retaining at least one fiberbore forming pin and at least one guide pin bore forming pin, saidassembly comprising a unitary member made from a single block of a rigidmaterial and defining at least one fiber bore and at least one guide pinbore, wherein said at least one fiber bore is created by an electricdischarge machining (EDM) wire, said unitary member comprising a frontface and a relief cavity disposed opposite said front face, said atleast one fiber bore extending in a lengthwise direction between saidfront face and said relief cavity.
 2. The guide block assembly of claim1, wherein said at least one fiber bore is formed by creating a starterhole with a first EDM wire and enlarging said starter hole with a secondEDM wire.
 3. (canceled).
 4. The guide block assembly of claim 2, whereinthe first EDM wire is connected to an EDM machine at one end and whereinthe second EDM wire is connected to the EDM machine at both ends. 5.(canceled).
 6. The guide block assembly as set forth in claim 1, whereinthe at least one fiber bore has a length and a diameter and wherein aratio between the length of the at least one fiber bore to its diameteris approximately 3::1 to 10::1.
 7. The guide block assembly as set forthin claim 6, wherein the ratio between the length of the at least onefiber bore to its diameter is approximately 4::1 to 8::1.
 8. The guideblock assembly as set forth in claim 7, wherein the ratio between thelength of the at least one fiber bore to its diameter is approximately6::1. 9-11. (canceled).
 12. A method for fabricating a guide blockassembly defining at least one fiber bore for aligning and retaining atleast one fiber bore forming pin, said method comprises the steps of:providing a blank made from a single block of a rigid material andcomprising a front face and a relief cavity opposite the front face, theat least one fiber bore extending in a lengthwise direction between thefront face and the relief cavity; securing said blank to a wire electricdischarge machining (EDM) machine; forming at least one starter hole insaid blank with a wire attached at one end to the EDM machine; andenlarging the at least one starter hole to a predetermined size anddimension of the at least one fiber bore.
 13. The method as set forth inclaim 12, wherein the enlarging step comprises the steps of: threading asecond wire through the at least one starter hole; and connecting bothends of the second wire to the EDM machine to enlarge the at least onestarter hole. 14-23. (canceled).